Process for the manufacture of continuous castings



Jan. 27,, 1970 B. TARMAQ ET L 3, 9 ,3

PROCESS-FOR THE MANHFAQTURE OF GONTINUOUS CASTINGS .Filed 001:. 13, 1966INVENTORS: 5 Gru THRMH NN Hevn a voNeANK mama ATTORNEY United StatesPatent 3,491,823 PROCESS FOR THE MANUFACTURE OF CONTINUOUS CASTINGSBruno Tarmann, Kapfenberg, Styria, and Heinrich Vonbank, Leobeu, Styria,Austria, assignors to Gebrueder Boehler & Co. Aktiengesellschaft,Vienna, Austria, a corporation Filed Oct. 13, 1966, Ser. No. 586,494Claims priority, application Austria, Apr. 22, 1966, A 3,786/66 Int. Cl.B2211 11/00 U.S. Cl. 164-76 5 Claims ABSTRACT OF THE DISCLOSURE Aprocess for the manufacture of strands of molten metal, in particularnonalloyed and alloyed steels, by continuous casting, in which the metalis worked while still in a partly molten condition, by means of aworking installation arranged downstream from the casting mold. Theimprovement of the process resides in working that portion of thehardened strand in which there is situated a liquid core having athickness of 5 to 30 mm., independent from the cross-sectional areathereof. The strand is worked in such a manner and to such an extentthat the cross-section is reduced by at least 20% and the leading end ofthe liquid core is formed upstream from the plane in which said strandattains its final cross-sectional configuration due to the workingthereof.

This invention relates generally to a method of continuous casting ofmolten metals, and in particular of nonalloyed and alloyed steels.

It is known that during the continuous casting of steel only theexternal peripheral zone of the strand is brought to a hardenedcondition in the ingot mold. The liquid interior, that is to say theso-called liquid pool or core, attains, with todays rapid continuouscasting techniques, a depth i.e., length of about 5 to 15 meters. It is,furthermore, known that strong convection currents take place in theliquid core within initially prevent the formation of strong liquationsand segregations. However, as soon as the diameter of the liquid core isdecreased to a thickness of 5 to 30 mm., due to a concomitant increaseof the external hardened zone, the convection currents lose theireffectiveness, which manifests itself by the formation in the core ofthe strand of soft spots, shrinkages, cavities and liquations. Theseformed liquations and segregations cannot be removed by subsequentprocessing of the continuously cast strands. This limits, in someinstances, the usability of the continuously cast strands.

In order to eliminate the afore-recited disadvantages, there has forexample, been proposed in the prior art to press together the travelingstrand by means of rollers at a point upstream from the naturalterminating point of the liquid core until the interior wall surfaces ofthe already hardened external zone shell are welded to the adjacentboundary layers between the external shell and the liquid core. This isbeing accomplished without creating a change of the wall thickness or astretching of the shell zone. In this manner, the formation of a slimliquid core can be avoided and the terminating point of the liquid coreextends to the axial plane of the rollers of the roller press. It hasbeen found that with this known process the aforerecited disadvantagescan be eliminated but a new undesirable side effect takes place, namelycracks and fissures appear in the interior of the strand, which cannotbe welded together during the further processing of the strand. (Theaforedescribed known process is disclosed in Austrian Patent No. 187,251and English Patent No. 766,584.)

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-It is therefore a general object of this invention to provide a novelprocess for continuous casting of molten metals in which all of theaforerecited disadvantages have been eliminated.

Experiments have indicated that during the working over of a strandwhich has not completely hardened, the formation of cracks and fissurescannot be absolutely avoided. It has, however, also been noted thatthese formed fissures and cracks are again subsequently welded togetherduring this same working process, if the working takes place in a regionof the strand, in which the liquid core thickness during hardeningwithout working amounts to 5 to 30 mm., and if the working results in asubstantial reduction in the cross-sectional area of the hardenedportion of the strand. In other words, if the liquid core headterminates as a point which, due to the working of the strand, ispositioned upstream from the plane in which the strand reaches its finalcross-sectional configuration due to the working thereof.

The working process according to this invention can be carried out withthe existing working installations for working strands, which aresuitable for reduction of the cross-section of materials. It ispreferred that the working is effected by means of rollers. The rollersof the driving installation in a continuous casting processing machinehave been found suitable for carrying out the process step of thisinvention. The rollens of the driving installation may have the usualdiameter that is prevalent in rolling mills of the described character.It has been found to be particularly advantageous to use grooved rollersin the fabrication of square and round strands.

It has also been found, in some instances, to be desirable not to permitthe distance between the ingot mold and the working installationoperating according to this invention, to become too large. It has,therefore, been proposed to provide a preworking installation whicheffects a preworking of the strand prior to the working processaccording to this invention. This preworking installation is arrangedbetween the ingot mold and the working installation of this invention.Due to this preworking step there occurs a reduction of thecross-sectional area of the liquid core, and the strand, consequently,attains sooner the liquid core thickness of 5 to 30 mm. which isrequired for the working process of this invention.

The continuously cast strand which has been worked in accordance withthe process of this invention has, after working, still a sufiicientlyhigh temperature so that, if necessary, it can by means of the usualknown steps be further deformed into the desired shapes and dimensions.

The conditions which must prevail during the process of this inventioncan be maintained without difficulties.

The prevailing thickness of the strand shell, i.e., of the liquid core,can be easily calculated on the basis of known formulas as for exampledescribed in the article by J. Savage and M. D. Ashton, Iron and Steel29 (1956), pages 229-235, so that the required distance between theingot mold and the working installation for a certain strandcross-section can also be easily determined. Preferably, the workingprocess according to this invention should be effected with steelshaving a large solidification period with a liquid core having athickness near the upper limit of the thickness range, whereas withsteels having a small solidification period the working process shouldbe effected near the lower limit of the thickness range of 5 to 30 mm.of the liquid core.

In the event there are produced strands having different cross-sectionalconfigurations and sizes, which generally would result in varying liquidcore lengths, the correct liquid core length can always be obtained byadjusting the rate of pouring of the molten metal or by adjusting thecooling rate of the strand.

Furthermore, the determination of the required size of the worked overarea of the hardened strand crosssection can be obtained withoutdifficulty, because the cross-sectional portion of the liquid core canbe calculated as well as the prevailing thickness of the liquid core. Inorder to shorten the liquid core length, in accordance with the processof this invention, to an extent that the liquid core point is positionedupstream from that plane in which the strand attains, due to the workingthereof, its final cross-sectional configuration, it is only necessaryto select such a large degree of deformation that it exceeds thecross-sectional portion of the liquid core. It has been found thatstrands of pronouncedly improved qualities can be obtained when thetotal cross-sectional area reduction during the working process of thisinvention is at least 20%.

The invention is illustrated by way of example in the accompanyingdrawings in which FIG. 1 is an elevated view of an installation forperforming the process according to this invention and FIG. 2 is a viewof the longitudinal section through the strand passing the pair ofrollers 5 in FIG. 1.

Referring to FIG. 1 there is shown an open ended reciprocating mold 1 inwhich the partial solidified strand 4 is formed. The strand emergingfrom the mold passes the cooling device 2, consisting of series of watersprays, and then runs through the insulated chamber 3, designed toreduce the temperature gradient of the solidified portion of the strand.The insulated chamber is followed by 4 pairs of rollers 5, 6, 7 and 8,which are employed for the reduction of the cross-section of the strand.

As a specific example, the following conditions are given for castingsteel (0.35 percent C, 0.06 percent Mn, 0.20 percent Si, the restsubstantially Fe):

Cross-section of mold mm. square 140 Radius of curved path of the strandm 6.5 Length of curved path of the strand m 10.0 Length of coolingdevice m 5.0 Length of insulated chamber m 2.0 Diameter of all rollers m0.4

If the strand is withdrawn from the mold at a speed of 1.8 111. perminute, it enters the first pair of rollers with a liquid core of 22 mm.in thickness. Passing the four pairs of rollers the strand is reduced tocross-sections of 150 x 95 mm. in the first, to 100 X 107 mm. in thesecond, to 110 X 72 mm. in the third, and to 80 mm. square in the fourthpair of rollers. The process of the invention is performed by the firstpair of rollers 5, by means of which the cross-section area of thestrand is reduced by about 32 percent, and whereby the reduction of thecross-section area of the solidified portion of the strand amounts toabout 30 percent.

As it is seen from FIG. 2, the liquid core 9 ends far before the centerplane of the two rollers 5.

In the foregoing, the invention has been described in connection with apreferred arrangement of a process thereof. However, since many othervariations and modifications will now become obvious to those skilled inthe art, it is accordingly desired that the breadth of the claims not belimited to the specific disclosure herein contained.

What is claimed is:

1. In a process for the manufacture of strands of molten metal, inparticular nonalloyed and alloyed steels, by continuous casting, wherethe metal is worked while still in a partly molten condition, by aworking installation arranged downstream from the casting mold, theimprovement comprising the step of working that portion of the hardenedstrand in which the liquid core thereof has a thickness of 5 to 30 mm.,independent from the size of the cross-sectional area thereof, in such away that the end of the core is formed upstream from the plane in whichsaid strand attains its final cross-sectional configuration due to saidworking, the cross-section of said hardened strand being reduced by atleast 20% by means of said working step thereby welding together thehardened strand shell so as to form a solid cross-section upstream fromthe transverse axis of said working installation.

2. The improvement as set forth in claim 1, wherein said working iseffected by a plurality of rollers.

3. The improvement as set forth in claim 2, wherein said rollers are ofstandard diameter and are operatively mounted in a driving arrangement.

4. The improvement as set forth in claim 3, including the step ofpre-working said strand and thereby reducing its cross-sectional areaprior to the step set forth in claim 1.

5. The improvement as set forth in claim 4, including furthercontinuously working said strand after the step set forth in claim 1.

References Cited UNITED STATES PATENTS 705,721 7/1902 Trotz 1642703,147,521 9/1964 Boehm 16470 3,237,251 3/1966 Thalmann 16489 X 3,307,2303/1967 Goss 164282 X FOREIGN PATENTS 187,251 10/1956 Austria. 58,4987/1953 France.

I. SPENCER OVERHOLSER, Primary Examiner R. SPENCER ANNEAR, AssistantExaminer US. Cl. X.R. 16482

